Oxidation and chlorine recovery process



Jan. 12, 1954 F. S. LW ET AL OXIDATION AND CHLORINE RECOVERY PROCESSFiled April 22. 1949 Patented Jan. 12, 1954 UNITED STATES PATENT OFFICEOXIDATION AND CHLORINE RECOVERY PROCESS Application April 22, 1949,Serial No. 88,954

2 Claims.

This invention relates to a process and apparatus involving a solutioncontaining hydrochloric acid and polyvalent metal chloride to bealternately oxidized from a lower state of valence to a higher state oivalence, and reduced from a higher state of valence to a lower state ofvalence with liberation of chlorine, said process being adapted to beused, for example, in a system and process for recovering chlorine fromhydrogen chloride.

In the oxidation oi a polyvalent metal chloride from a lower state ofvalence to a higher state of valence in a hydrochloric acid solution, byblowing air or oxygen therethrough, water is formed in the reaction andconsiderable I-ICl will he carried out with the spent oxidizing gases.It is necessary to remove the formed water from the solution and also toreturn t-o the solution or liquor stream, the HC1 carried over with thespent gases from the oxidation step,

Such an oxidation process is useful for Various purposes and one ofthese is that in which there is a problem of recovering chlorine fromwaste hydrochloric acid such as described in the patents to Frank S.Low, Nos. 2,4%,766 and 2,470,073, issued on May 3, 1949, and May l0,1949, respectively. The recovery oi chlorine from waste hydrochloricacid always has been a problem, particularly because of the large numberof industrial processes wherein hydrochloric acid is an unavoidableproduct. Direct electrolysis of hydrochloric acid and recovery by theDeacon process have not been satisfactory or economically feasible forthe purpose. In the process described in said copending patents,polyvalent metal chloride, such as cupric chloride, ierric chloride, andother suitable polyvalent metal chlorides are electrolyzed in a cellsuch as oi the type described therein, the aqueous solution to beelectrolyzed containing HC1 and polyvalent metal chloride in an oxidizedstate. A portion of the polyvalent metal chloride is reduced in the cellso as to liberate chlorine which can be recovered in conventionalmanners. The concentrations of the solution or liquor involved should bekept Within certain limits as they tend to be critical in character. Thesolution containing` the reduced inetal chloride is then passed into anoxidation apparatus or zone wherein the following reaction takes place:

It is seen that in such an oxidation process, water is formed and thiswater must be removed from the system so as to preserve the properbalance and concentrations, particularly to obtain optimum results, thisbeing oi special `irriportance in the commercial operation of theprocess. Also HC1 is carried over with the gases employed in theoxidation and the water removal step, thus requiring measures to recoverthis HC1.

A portion of the polyvalent metal chloride solution is reduced in anelectrolytic cell.. The formed gaseous chlorine is removed from the cellas is also the reduced electrolyte.

One of the objects is to provide an improved economical process forrecovering oi chlorine values from hydrogen chloride by an electrolyticreduction and a subsequent oxidation process.

Another oi the objects of this invention is to provide an improvedmanner of operating a polyvalent metal chloride-hydrochloric acidsolution oxidation process, so as to remove the water formed during theoxidation step and recover the HC1 carried over by the spent gases.

The invention will be described in conjunction with an electrolyticprocess for the recovery of chlorine. In general, the polyvalent metalchloride in a higher state of valence in the aqueous hydrochloric acidsolution is fed into an electrolytic cell or bank of cells, said cellsbeing constructed, for example, in accordance with the disclosures insaid aforementioned patents. In such cells, a porous cathode uniformlyspaced from the anode is employed, chlorine being withdrawn from saidelectrolytic cells as it is formed. The solution containing reducedpolyvalent metal chloride is introduced into and carried through anoxidation process, the arrangement oi which forms part of the subjectmatter oi this invention. The oxidation apparatus is arranged so thatair is pumped therethrough to reoxidize the polyvalent metal chloride toits higher state of valence and to remove the formed water.

In a preferred aspect of the invention, a series of tanks is employedhaving agitating means therein. In this oxidation process, water isformed and must be removed so as to maintain the correct concentrationswhen the liquor or electrolyte is returned to the electrolytic cells.The gases passing through the oxidation tanks also are used to removethe water formed during the reaction but these gases also will removesuicient quantities of HCl to require ior optimum economy in operationthat provision. be made to return the HC1 to the system. One manner ofaccomplishing the return of the HC1 is to remove the Water from theoxidation step vent gases and then contact the dried vent gasescontaining the HC1 with at least a portion of the solution being passedthrough the agitated oxidizing tanks so as to reabsorb the HC1 in saidsolution.

ln a preferred form, a portion of the solution containing the polyvalentmetal chloride therein to be re-oxidized is diverted from the liquorstream before it reaches the last oxidizing zone or tank, cooled, andbrought into contact with the vent gas from the various oxidation tanksafter the water has been removed from*r said gaathereby absorbing theI-lCl and returning it to the main liquor stream.

Another object of the invention is to provide an improved manner ofoperating theoxidationA tank vent gas drier arrangement so that it willbe substantially adiabatic.

This aspect can be accomplished by utiliz-` ing the heat generated in`the exothermic reaction in a drier zone or apparatus employing H2SO4. Byconnecting the drier. arrangement with an evaporating and a condensingdevice and` properly insulating this part of the'systein, asubstantially adiabatic: process can be obtained. The heat generated inthe vent gas drier will be available for evaporation in an evaporatorarrangement for separating the sulphuric acid from the water removedfrom` the Vent gases. The water then can be condensed for. disposal. Abarometric condenser and evaporator can. be used for the aforementionedpurpose of evaporating and condensing.

When the oxidation system is usedin conjunction with an electrolyticcell arrangement for recovery of chlorine, automatic controlsl can beutilized wherein the outilow rate or volume of chlorine is employed togovern the inflow of hydrochloric acid in the correct proportions tomaintain the desired and optimum concentra.- tion of HCl in the systemat all times, such a control and maintenance of concentration inconjunction with efficient water removal insuring a satisfactory andeconomicalI operation. It is to be understood that other methods ofcontrol can be used.

These and other advantages, objects, and features ofthe invention willbecome apparentv from the following description and drawings.

Figure 1 illustrates a complete system for the recovery of chlorine fromhydrochloric acid- Figure 2 is a sectional view of oneformofelectrolytic cell which can be usedv in the system of Figure l.

Describing generally the system ofl Figure 1, the aqueous solutioncontaining polyvalent metal chloride in its higher state of valencetogether with hydrochloric acid is fedinto an electrolytic cellarrangement. The hydrochloric acid` in the solution serves to increasethe solubility of the metal chloride in the solution and. also as asource of chlorine in the process to badescribed hereafter. In theelectrolytic cell arrangement, the polyvalent metal chloride-isreducedfrom a higher state of Valenceto a lower state of val.-

ence and the chlorine is formed thereinand re` The electrolyte containThe vent gases from the various oxidation.

tanks are collected, said vent gases containing the water formed in theprocess together with the HC1 carried over from the `oxidation zones.The oxidation tank vent gases are then subjected to a drying process forthe purpose of removing the contained water. The dried gases arethereafter contacted-Withk at least. a portion of the liquor streamcontaining; the polyvalent metal chloride so as to reabsorb the HC1 intosaid stream.

In a preferred form, a portion of the liquor stream utilized forreabsorbing the HC1 from the spent oxidation gases is diverted from thesystem beforethe last oxidation tank is reached and then thedivertedportion with the reabscrbed HC1 is returned to the system in the lastoxidation tank, together with hydrochloric acid equivalent to. theamount of chlorine used in the preceding electrolytic step. In such anarrangement, it is possible to use the outflow of chlorine to controlthe inflow of HC1 into the system so. as to maintain the properconcentrations of HC1, water, and polyvalent. metal chloride.

One type of suitable electrolytic cell-arrangement will be described,reference being made to said aforementionedv patents. lhe electrolyticcell illustrated at I (Figs. l, 2) may have an anode Il' ofsubstantially impervious graphite.V The cathode l is formed of a porousgraphite or any good grade of porous conducting carbon. Merely by way ofexample, a satisfactoryporous material is one having a permeability ofabout 30 gallonsof water per square foot per minute at 5 lbs. per squareinch pressure; although cathodes having' as high a permeability as 175gallons per square foot per minute at 5 lbs. per square inch pressureand as low as 0.3 gallonv perv square foot per minute at 5 lbs. persquare inch presev4 sure may be used provided the system is properlyarranged. rihe above permeabilities are based onthe llow of water at '70F. through graphite which is 1ll thick.

The use-of aporous graphite cathode eliminates the necessity of adiaphragm, and this omission removes one of thev principal difcultiesWhich is ordinarily. encountered in the electrolyzing of hydrochloricacid. solutions directly.

There are only a few materials which are satis-l factory for use asdiaphragm media. inal solu tion containing substantial quantities ofhydrochloric acid. Even acid leachedasbestos tends to disintegrateslowly in such a solution and glass wool tends to dissolve slowly in thesolution. By eliminating the diaphragm, the cell construe? tionV isgreatly simplified, and thevoltage requirements of the cell are reduced.

The electrodes l! and I2 may be concentric. or may be flat as desired,it being desirable that-` the active surfaces of the cathode and anodeshould be spaced apart substantially the same distance over their entireactive area. so, as to obtain the most efficient results in theelectro.- lytic cell. A uniform electroly-tic gap of between about 1/2to 1" is desirable.

The electrolyte is introduced through pipe I3 (Figs. 1, 2) into theanolyte chamber I4 (Fig. 2) between anode Il and cathode l2. Plug orcover I5 can be shaped so as to form a cover for the catholyte chamberIE5, it being noted that the level l1 of the anolyte i4 in the anolytechamber should be made slightly. higher than the level I8- The formedchlorine is removed chamber I4. Catholyte is removed through pipe 22 andgooseneck 2l, said gooseneck serving to maintain the correct level inthe catholyte chamber and thereby producing the desired flowcharacteristics through the porous cathode, it being apparent that othertypes of level control can be used. In the construction illustrated,there will be no seepage of chlorine through the porous cathode. Theelectrolyte ilow to the cells can be controlled if desired, as by theinsertion of tubing sections 22 of appropriate bore, in the supply linefrom constant head tank 23. The upper portion of the electrodes may beimpregnated with a substance such as a mixture of chlorinatednaphthalenes to prevent chlorine seepage. The electrodes may be sealedto the base plate of the container by high melting pitch or othersuitable material.

The electrolyte composition may have up to about 25% HCl by weightconcentration but should not be less than about 5%. There will tend tobe an excessive carry over in the formed chlorine when the HC1concentration is above 25% and the resistance of the electrolyte willrise rapidly when below 5% so as to cause excessive power consumption inthe cell.

The polyvalent metal chloride, for example, can be copper chloride, ironchloride, or chromium chloride, these being oxidizable from a lowerstate of valence to a higher state of valence. The polyvalent metalchloride also must be reducible in the electrolytic cell from a higherstate of valence to a lower state of valence.

It is preferable to keep the concentration of the polyvalent metal saltin the electrolyte above 5%, the upper limit for the concentration beingthe solubility of the polyvalent metal chloride in the electrolyte. Inthe case of cupric chloride at room temperature in a solution containing20% HC1, the upper limit is about 17% by weight of cupric chloride andis not less than about 18% for ferrie chloride. At higher temperatures,the solubility of the chloride becomes higher. It is possible to uselower concentrations but generally when below 5% by weight of cupric orferric chloride is used, an excessive amount of liquor or electrolytemust be circulated. The optimum concentration of cupric chloride in theelectrolyte is about and of ferric chloride about 18%. An electrolyte ofapproximately 15% by weight of cupric chloride and 20% by weight ofhydrogen chloride has high chlorine producing capacity, thisconcentration also having low corrosiveness with respect to the graphiteof the electrolytic cells and high electrical conductivity. In respectto graphite corrosion, it is desirable, although variations may be made,that the concentration of HC1 should not be below about 10% for a 5%cupric chloride concentration in order to avoid excessive wear of theelectrodes during electrolysis.

The high acidity keeps the metallic chloride in solution and eliminatescathode plugging difficulties or deposition of salts in the circulatinglines. If the acid concentration in the electrolyte is not maintainedsufficiently high to prevent the precipitation of insoluble compounds atthe cathode, the voltage of the cell will slowly rise and the powerconsumption of the cell will become excessive. Accordingly, it is animportant part of the invention to maintain the hydrogen chlorideconcentration in the electrolyte at a high level, preferably within therange noted hereinabove.

The chlorine gas leaving the cell is collected in pipe or header 24 andfed to a chlorine cooler 25 through pipe 26. The cooled chlorine gas isfed through pipe 21 to the chlorine drier 28, the gas being removedtherefrom through a suitable pump 29 to the outlet pipe 30. ConcentratedH2804 may be fed through pipe 3l to the drier for the purpose of dryingthe wet chlorine gas. As will be explained hereafter, a iiow controlarrangement 32 responsive to the flow at 32A of the chlorine from thesystem can be used to control the addition of HC1 to the system byregulating valve 33.

The cell eiiluent or liquor can flow from the cells through pipe 34 tothe sump 35, said sump having a pump 36 for pumping the liquor throughpipe 31 into the first oxidation tank 33. A flow control valve 39 can befurnished responsive to the level in the rst oxidation tank to controlthe flow of liquor to the rst tank.

The oxidation tanks should have suitable agitator impellers therein andair is blown therethrough from a blower 80, said blower feeding air toheader 40 which is connected to each of the oxidation tanks. Fiveoxidation tanks or zones are shown but it is understood that a greateror less number of tanks may be employed. The flow of air can becontrolled by a suitable by-pass 8|. The oxidation tanks can be of thedescribed and preferred agitated tank type having suitable agitatingimpellers or similar arrangements therein, although other types ofdevices can be used such as packed towers or diffusers.

It can be theorized that in the oxidation of a material such as cuprouschloride to cupric chloride in an HC1 solution with oxygen from the air,several processes take place. First, the oxygen in the air diffusesthrough the gas rllm to the liquid surface and there it dissolves andthen diffuses through the liquid film into the cuprous solution.

The oxidation tank spent or vent gases con-V taining water vapor and HC1are removed through pipes 4| to a common header 42. The partiallyreoxidized liquor eiluent from tank l is fed by pipe 43 into the secondoxidation tank and this is repeated in the various oxidation tanks untilnext to the last tank is reached, the dow between the tanks beingarranged to take place by gravity if desired. The oxidation tank spentgas containing water vapor and HC1 is collected and can be fed throughan entrainment trap 154 into a vent gas drier arrangement 15.

As previously mentioned, the oxidation tank vent gas drier can be madeso that advantage is taken of the excthermic reactions involved.Concentrated sulphuric acid is fed through pipe 48 into said drier bypump ll.

A barometric type evaporator and condenser arrangement is has a weaksulphuric acid efiluent from the vent gas drier fed thereto through pipe5U and heater 5l. Heater 5l can be employed to furnish any additionalheat if required. rlihe evaporator d2 and condenser 55 operate undervacuum, which makes it possible to utilize the heat generated when watervapor is absorbed in the sulphuric acid in tower (t5 to revaporize orflash off the water in evaporator 52. The vacuum is maintained bycondensation of water vapor in condenser 55 by direct contact with coldwater, and by removal through ejector 5l oi any noncondensible gasesthat enter the system.

The eluent passing into barometric evaporator 52 has the water iiashinto vapor therein, said vapor being carried through entrainment trappassage 54 to water condenser 55. The reto apacked column arrangement`or HClfabsorber 5.3 through pipe E38. Af portion oftheipartially.vreoxidized liquor is removed from the systemat. 0l' by'pump G2. and'edthrough pipe 63'int0the absorber 5e, cooler being provided. Cooler.r@d is necessaryy inasmuch` asthe HCl'couldlnot be reabsorbediin a hotlsolution. Thel absorbing solution must be at a` lower temperature thanthe liquor in the oxidationtanks. A4 flow control valve S2 responsive totheliquor return-temperature can be providedfto control the amount ofthe liquor stream fed tothe'HClf absorberI col-- umn 59; Most or the HCland'- remaining Water is removed from the-ventl gases in the HC1absorberI 5e and returned throughl pipe 65 to the last oxidation towerWhere it rejoins theremainder of* the partially oxidizedvliquorstreamfed thereto by pipe 6d from next tothe lastI oxidation tank.A-portionor all-of the-liquorstream can be diverted from the system atsome other'l suitablepoint other than between the nextVA to lastvand'last oxidation tank, but it is'preferred` to be accomplished in themanner described.

It is, of course, possible torecover-the HC1 and remove-Water in othermanners.

Anothermanner in which theH'zSO'i from the Vent gas driercouldbe-recovered-Wouldfbe by reccncentrating the same with combustion'gases such as in a packed, tower by means of heat, but such anarrangement` would havelarge fuel requirements.

The HC1 to be fed to the system to properly maintain concentrations,preferably is introduced into the system in the-last oxidation tank. Inone embodiment, relativelyl strong hydrochloric acid is fed by a pump Elthrough a feed preheaterfor heat exchanger 63 into a Packed distillationcolumn 69 or HCl expellerapparatus. The hydrochloric acid passeslthrough the column into a reboiler S3 so that it progressivelydecreases in HC1 content to approximately that of constant boiling acid.From column 69,- the hydrochloric acid iiows through feed preheater orheat exchanger E8' and'coolerlil-back totheprocess producing theby-product' HC1, Where it is enriched with HCl gas to produce relativelystrong hydrochloric acid for feeding to the HC1` expeller apparatus. TheHC1 rich vapors pass from thetop of the column 69 intov a partial'condenser li, condensate therefrombeing returned as reflux through line12 into the packed distillation column. The HCl gas` is carried throughline i3 and blown into the last oxidation tank l@ as described. Thereoxidation liquor is then carried through line l5, cooler 16, back tofeed tank 23. A continuous CuCl and CuClz analyzer can be provided at1li if` desired for the purpose of controlling the operation ofA thesystem, either manually or through suitable control mechanism connectedtherewith.

As agspecic example of one-manner in Which-` the described system. canbe operated in conjunction with the recovery'ofchlorine `from waste 85.hydrochlonic acid; a; systemmay be describedin which approximately223,000 lbs; by weight per hour; ofgliquor is fedto` the rst: oxidizer.For example, this liquor. may contain by weight, ap.- proximately 3.4%CuCl; 10..2%.CuCl2, 20.4% HC1, andy 66% `H2O.

A system for producing 35 tons per day or" chlorine Witha 341%hydrochloricV acid feed, could' use 5 agitated oxidation tanks withVimpellersvas described. Atotal-o '750.cubic feet per minute of free airat 4. lbs. per square inch being blown into the-oxidation. tanks, thisbeing divided'sothat: tanks. #1. and: #.2` each receive about 266cubicreet: per minute; tank #3, 135.` cubic feet' per.v minute; tank #4,56 cubic feet per minute, and tank #5., 27 cubic feet per minute. In,such an instance, the oxidationtanks can be operated so that the oxygenefiiciencies of tanks Nos. l to 5; would be about 81%., 81%, 79%., 79%vand 441%, respectively. Theeiciency values iorthe difiere ent` stagesvvary because oxygen absorptionrate controls during the iirstthree stagesandnreaction rates during the last .two stages.

Merelyby Way of example, the oxidationtankscan be made l2 feet? deep, 8'eettinside diameter, and each can be equipped with an agitator, balies,`and: an air sparger. The-rmaximumair rate which canbe usedei'lcientlywith suchatank, is*` about fl'eetzper minute` velocitybasedon` the tank cross-section area, this rate being`- useddn thefirst' two stag-es. The power input to eachoi the first threetanksyvould be about 40 horsepower, and for the last two tanks, 20horse- ,power each. The temperature in the first tank may be about 83 C.and' the temperaturein the.

last tank 94eY C. The tenflperature of the dried` vente gas being fed tothe vent gas reabsorber column dmay beabout C., andthe temperatureofthe-liquor efrluent' being returnedto. No. 5 oxidation tank mayj-beabout. '70 C; The

temperature of: the; liquor stream into the HC1;

absorber columnl 519'; may be'l about 40" C., cooler 64 loweringthetemperature-toV the desired value.

In one manner of' operating the processap, proximately 10 by Weight ofthe liquor stream. can be removedzor diverted from themain solution'stream'folloiving oxidation tank No. 4. This divertedv portion aftercooling4 to about' 40' C.' is. used tofrecoverorreabsorb' the HC1 intheoxida.- tion'tank'vent gases: t is, of course, to.be un.-

derstoodv that the proportion` removed. from, the.

main liquor stream for. HCll reabsorption pur,.- poses wilLdependuponthe specic operationothe` system.

Intheexample, the portionol the liquor: used' tofreabsorb HC1. fromthevent gasV can,y be taken-f from between.'oxidation-tank. #4L andi#5.. andre;- l

The;- liduoi used; for. this ,purpose turnedto #51.. should; havel a;relatively low. HC1` concentration,

and this condition is adequately met byk the- The oxidationrtowerventgases in thedescribed;

operation-may contain about.119.%. of the-Water.`

to be removed from the process and 22% of. theY HC1' fedfinto thesystem;y Ventgas drying tower i'imay be operatedsothat 93% of.` thewaterfto;V

be removed from the process is absorbed by the sulphuric acid.

The temperature of the cooling Water in the barometric condenser shouldnot rise above about 33 C. and a Vacuum of about 28 inches Hg should bemaintained therein. About 7% of the water to be removed from the systemand about 0.7% of the HC1 fed to the system may be lost through thewaste vent gas outlet 84 from the HC1 absorber 59. The rate of flow ofliquor to the absorber 59 may be controlled by the temperature of theliquor coming out of said absorber 59. The temperature of the liquorinto the absorber 59 may be used to control the water ilow to cooler 94.

When hydrochloric acid is involved in a chlorine recovery process, thedistillation column or HC1 expeller 69 may be operated so that when theinilow has a 34% HC1 concentration, the concentration of the return tothe HC1 storage tank will be reduced to about 21% HC1. In the operationof the electrolytic cells, the voltage may be 1.75 volts per cell andthe current eiliciency 81%, the current density being approximately 400amperes per square foot of cathode surface.

If desired, small coolers may be used between some or all of theoxidizers instead of the illustrated large cooler 16.

In the specific example described, with a total weight of liquorentering No. 1 oxidizer of about 223,000 lbs. per hour, 3100 lbs. perhour of 98% HC1 ctn be fed to No. 5 oxidation tank and about 2900 lbs.per hour of C12 withdrawn from the process.' In such a process,approximately 2200 lbs. of liquor are fed to the Vent gas reabsorbertower 59. About 41,500 lbs. per hour of 76% l-12S04 is required in thevent gas drier, the sulphuric acid being fed at about 115 C. into saiddried and being raised to 144 C. in the drier or by an addition of heetas it passes through heater l before it is introduced into thebarometric evaporator 52.

It is to be understood that various types of apparatus may be used whichwill affect the quantities and temperatures involved and that the aboveis merely one example of the manner in which the oxidation processdescribed herein may be employed.

The oxidation portion of this invention may be used in other processes.

The process and apparatus may have details thereof varied withoutdeparting from the spirit 10 of the invention except as dei-ined in theappended claims.

What is claimed is:

1. In a process for recovery of chlorine values from hydrogen chloridepresent in the used electrolytic solution of a chlorine cell operatingon an aqueous electrolyte containing hydrogen chloride and the chlorideof a metal capable of existing in differing ionic valence states, saidmetal being at least in part reduced during electrolysis from a higherto a lower valence state, the improvement comprising: transferring saidcell solution to an oxidizing zone; intimately contacting the cellsolution in said oxidizing zone With gas containing elemental oxygen fora time sufficient to substantially effect (l) oxidation of hydrogenchloride with simultaneous formation of water and conversion of metalfrom a lower to a higher valence state, and (2) volatilization of Waterfrom the cell solution; dewatering hydrogen chloride-containing ventgases discharged from the oxidizing zone; withdrawing oxldized cellsolution from the oxidizing zone; cooling the withdrawn cell solution toa temperature substantialiy below that obtaining in the oxidizing zone;contacting said vent gases with cooled oxidized solution; introducingadditional hydrogen chloride into the oxidized cell solution in anamount approximately equal to the amount oxidized in the oxidizing zone;and finally returning the reconstituted cell solution to the chlorinecell.

2. The process of claim 1 wherein only a portion of the oxidized cellsolution is withdrawn from the oxidizing zone; cooled; contacted withthe dewatered vent gases; and then reunited with the remainder of theoxidized cell solution discharged from the oxidizing zone.

FRANK S. LOW.

CHARLES P. ROBERTS.

References Cited in the file of this patent UNITED STATES PATENTS NumberName Date 741,637 Dow Oct. 20, 1903 850,695 Vermeesch Apr. 16, 19071,198,519 Bradley Sept. 19, 1916 1,207,243 Vadner Dec. 5, 1916 1,553,223Dietzsch Sept. 8, 1925 1,917,226 Bacon et al July 11, 1933 2,312,952Balcar Mar. 2, 1943 2,468,766 Low May 3, 1949

1. IN A PROCESS FOR RECOVERY OF CHLORINE VALUES FROM HYDROGEN CHLORIDEPRESENT IN THE USED ELETROLYTIC SOLUTION OF A CHLORINE CELL OPERATING ONAN AQUEOUS ELECTROLYTE CONTAINING HYDROGEN CHLORIDE AND THE CHLORIDE OFA METAL CAPABLE OF EXISTING IN DIFFERING IONIC VALENCE STATES, SAIDMETAL BEING AT LEAST IN PART REDUCED DURING ELECTROLYSIS FROM A HIGHERTO A LOWER VALENCE STATE, THE IMPROVEMENT COMPRISING: TRANSFERRING SAIDCELL SOLUTION TO AN OXIDIZING ZONE; INTIMATELY CONTACTING THE CELLSOLUTION IN SAID OXIDIZING ZONE WITH GAS CONTAINING ELEMENTAL OXYGEN FORA TIME SUFFICIENT TO SUBSTANTIALLY EFFECT (1) OXIDATION OF HYDROGENCHLORIDE WITH SIMULTANEOUS FORMATION OF WATER AND CONVERSION OF METALFROM A LOWER TO A HIGHER VALENCE STATE, AND (2) VOLATILIZATION OF WATERFROM THE CELL SOLUTION; DEWATERING HYDROGEN CHLORIDE-CONTAINING VENTGASES DISCHARGED FROM THE OXIDIZING ZONE; WITHDRAWING OXIDIZED CELLSOLUTION FROM THE OXIDIZING ZONE; COOLING THE WITHDRAWN CELL SOLUTION TOA TEMPERATURE SUBSTANTIALLY BELOW THAT OBTAINING IN THE OXIDIZING